Lomandraspiny-headed mat-rushinflorescenceis derived from the Greek λωμα (loma), the border of a robe, and ανηρ (aner), a man, referring to the borders on the anthers of some species; longifolia is from the Latin longus, long, and folium, a leaf.

The Spiny-headed Mat-rush is a rhizomatous sedge-like plant, forming dense tussocks of stiff, long, flat (or slightly rolled inwards), nearly parallel-sided leaves up to about 1 cm wide. The leaves are shiny, 40–100 cm long, and are usually taller than the flowering stem. Normally the ends of the leaves are either 2- or 3-toothed, but there is great variation in the species, depending on locality and growing conditions.

The plants are dioecious. The stalkless flowers, which are scented, are in a dense spike-like inflorescence up to 50 cm long, containing dense clusters of tiny flowers along the flattened stem, each cluster having a sharp slender straw-coloured bract near its base. Individual flowers are about 4 mm long, with the female flowers often a little bit longer or larger than the male flowers; the sepals are shiny brown, thin and papery; the petals are fleshy and creamy yellow, sometimes purplish in the centre. The heavy-smelling nectar on the flowers can attract pollinating beetles. The flower head is followed by brown seed capsules. The plants flower from August to December, with seed heads lasting at least several weeks on the flower stalks.

This relative of the grass tree is found in many different habitats in the eastern states of Australia, from sand dunes, open forest, creek banks to rainforest. When it is not in flower, it can be difficult to distinguish from a grass. There are quite a few of the plants in island gardens, and there are others growing in waste land at the southern end of Picnic Street.

The plant is suitable for growing indoors in containers as well as outdoors, and requires moist soil for growth. However, its thick leaves and rhizomatous root system help it, once grown, to tolerate dry periods. It is propagated either by seed or by division.

Aboriginal people use the leaves of the plant to make strong nets, baskets and mats, and they eat the base of the leaves as food.